There are already known various constructions of electric motors and generators (collectively referred to herein as electric power devices), among them such employing commutator arrangements for either supplying electric current to, or withdrawing electric current from, a plurality of windings that are mounted on a rotor of the electric power device for rotation therewith. A commutator arrangement of the above type typically includes a commutator ring which is usually mounted on the rotor of the electric power device for rotation therewith, and a plurality of so-called commutator brushes which are usually mounted on the stator of the electric power device and are in electrically transmissive contact with the commutator ring. The commutator brushes are mounted on the stator for movement in the respective radial directions and are biased toward the commutator ring to assure as good an electric contact therewith as possible without unduly interfering with the rotation of the rotor. The commutator ring includes a plurality of circumferentially adjacent contact pads which are individually electrically connected with the respective associated windings of the rotor and are electrically separated from one another by respective gaps which are usually at least partially filled with a solid dielectric material.
The circumferential extent of each of the brushes is usually greater than that of any of the gaps, so that the respective commutator brush is in contact with either a single one, or two circumferentially adjacent ones, of the contact pads of the commutator ring, thus electrically bridging the intervening gap in the latter instance. To avoid excessive sparking and/or electric power loss, the contact pads of the commutator ring are associated (electrically connected) with their respective windings in such a manner that the electrical potentials to be supplied to (if the electric power device is a motor, to power the same), or appearing at (if the electric power device is a generator), any two circumferentially adjacent ones of the contact pads are only insignificantly different from one another during such bridging.
It will be appreciated from the above that the presence of the electrically insulating gaps on the commutator ring, and the movable mounting and biasing of the brushes, are essential for the operation of the commutator arrangement. However, experience has shown that the combination of these features results in the generation of objectionable high-pitch or whining noises, at least in small-size electric motors, during the operation of such devices when they are constructed in accordance with the current practice. When looking for the source of such noises, it was established that they result, at least in part, from the fact that, be it because of manufacturing inaccuracies, or due to wear, or as a result of the very existence of the gaps, the area of the circumferential surface of the commutator ring with which the respective commutator brush is in contact undergoes movements in opposite radial directions as the commutator ring rotates relative to the brush. Now, because the commutator brushes, despite their name, are nowadays usually constituted by solid bodies, the aforementioned radial movements are followed by the brushes, resulting in vibrations and attendant noise.
Moreover, because both the commutator pad edges and the commutator brush edges extend parallel to the axis of rotation in the heretofore known commutator arrangement constructions in order to minimize the duration of the aforementioned electrical bridging, additional movements (and noises) may be induced in the respective brushes as their edges run into or dissociate themselves from the corresponding edges of the respective commutator pads over their entire lengths at the same time. While this particular problem could be minimized if not eliminated altogether by filling the gaps of the commutator ring with the solid dielectric material to such an extent that the affected surfaces of the thus obtained dielectric material separators constitute, at least initially and possibly after machining, smooth continuations of the contiguous contact surfaces of the adjacent commutator pads, even the adoption of this measure still does not eliminate the noises resulting from the commutator brush movements attributable to the radial deviations of the contact surface of the commutator ring from its ideal cylindrical configuration centered on the axis of rotation and, if steps are present between the adjacent edges of the pads, especially those caused by the meeting and dissociation of the brush and pad edges.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a commutator arrangement which does not possess the disadvantages of the known arrangements of this kind.
Still another object of the present invention is so to develop the commutator arrangement of the type here under consideration as to minimize if not eliminate noise generated as the commutator brushes ride on the corresponding commutator ring surface.
It is yet another object of the present invention to devise an arrangement of the above type which would maintain the efficiency of the device employing the same at a relatively high level.
A concomitant object of the present invention is to design the commutator arrangement of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.